Clay bricks are fired in kilns at high temperatures for 10 to 40 hours, depending on the kiln type and other variables, to achieve the necessary strength and durability. The two most common types of kilns used are tunnel kilns and periodic kilns. The fuel source can vary, including natural gas, coal, sawdust, or methane gas from landfills, or a combination of these.
Here's a more detailed breakdown:
-
Kiln Types:
- Tunnel Kilns: These are continuous firing systems where bricks move through a long tunnel on rail cars. Different zones within the tunnel maintain specific temperatures for preheating, firing, and cooling.
- Periodic Kilns: These are batch kilns where bricks are loaded, the temperature is raised and held for a specific time, and then allowed to cool before unloading.
-
Firing Process: The firing process involves several stages:
- Water Smoking: The initial stage involves slowly heating the bricks to remove any remaining moisture.
- Oxidation: As the temperature increases, organic materials in the clay are burned off.
- Vitrification: This is the crucial stage where the clay particles fuse together, giving the brick its strength and durability. This happens at peak temperatures.
- Cooling: The bricks are slowly cooled to prevent cracking.
-
Fuel Sources: The fuel used for firing can vary based on availability and cost. Common fuel sources include:
- Natural Gas
- Coal
- Sawdust
- Methane Gas (from landfills)
-
Firing Time: The total firing time can range from 10 to 40 hours, depending on the type of kiln, the size of the bricks, and the desired level of vitrification.
